The photograph shows a sample of stained frog blood cells as viewed with the high-power objective of a compound light microscope, with a specific structure labeled "A". Which of the following is the BEST description for the structure labeled "A?"
A Chloroplast that carries out photosynthesis
B Lysosome that stores hydrolytic enzymes
DC Mitochondrion that produces ATP
OD Nucleus that regulates cell activity

How can you keep track of variables in a science experiment?

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area

Which direction does the energy flow in this energy pyramid ?